A continuing objective in the manufacture of integrated circuits is to reduce the dimensions of the circuit elements to produce the highest possible density. In the manufacture of MOS integrated circuits it is the usual practice to separate active areas of the semiconductor by use of isolation oxidation which is also referred to as field oxide. In the conventional method of fabricating the isolation oxidation, a 1,000 angstrom thick pad oxide is fabricated on the surface of a semiconductor substrate with a 1,000 angstrom thick nitride layer fabricated over the pad oxide. The nitride layer is etched to expose an open area and the isolation oxidation is grown in this area. This manufacturing process yields a minimum of oxidation induced defects but produces a long sloping edge structure which is referred to as the "bird's-beak" area. There is typically a 1:1 ratio between the length of the bird's-beak area and the thickness of the isolation oxidation. The bird's-beak area expands the width of the isolation oxidation which substantially limits the minimum dimension which can be produced for the isolation oxidation.
In view of the above problem regarding the bird's-beak area produced in the conventional fabrication of isolation oxidation in MOS circuits, there exists a need for a manufacturing process for the production of isolation oxidation with a much shortened bird's-beak area to reduce the dimensions of MOS elements.